544 



J. F. JBLAKE ON THE UPPER 



Portlandian, 280 ft. 

 Gypseous beds. 

 Lumachelle limestones. 

 Tabular compact limestones. 

 Alternations of compact limestones. 



Kilnmeridgiaii, 260 ft. 



White chalky limestone. 

 Marls with Exogyra virgula. 



Corallian, 330 ft. 



Coral limestones. 

 Limestone with Nerineeece. 



Oxfordian, 550 ft. 

 Shaly marls. 



Clays and marly limestones. 



"Whether the rocks in the Lower Charente are really different 

 from those in the Upper, or whether their exposure in the sea- cliffs 

 gives a better opportunity for judging differences, certain it is that 

 in the neighbourhood of La Rochelle one is immediately aware that 

 one is studying the development in a new basin, and things are 

 changed. If, in fact, we examine the lists of d'Orbigny as given 

 in his ' Prodrome,' we find that out of 222 Corallian species from this 

 locality, no fewer than 90, or more than 40 per cent., are peculiar, 

 while only 80 occur in any of the localities yet studied. 



The Oxfordian strata are of particular interest as occurring at 

 Marans, whence the name of Ammonites marantianus is derived, 

 which indicates that we should expect the overlying "Limestones with 

 Nerinoeae" to belong to the true Corallian series. The lower portions of 

 these occur on the north side of La Rochelle ; but the upper portion 

 is the more fossiliferous, and occupies the first two headlands to the 

 south, viz. the Point des Minimes and the Point de Eoux. Here they 

 are very marly, with beds of limestone crowded with cavities formed 



Pig. 13. — Map of the Coast round the Pertuis cV Antioch. 

 (Scale 1 : 240,000.) 



